Generally, as the support members of rotation shafts of devices, apparatuses, etc., often used are bearings of which the outer ring and the inner ring are relatively rotatable. As the above bearings, so-called rolling bearings, such as ball bearings, roller bearings, and needle bearings are widely known, for example.
Generally, in business machines and image forming apparatuses, a rotation shaft of each roller which conveys printing sheets is arranged between a pair of frames, panels, etc., and the ends of the rotation shaft of the roller is supported by bearings attached to the frames, panels, etc., for example, by ball bearings. The rotation shaft is supported by fitting it at the ends thereof to the inner rings of the bearings. For this fitting between the rotation shaft and the inner rings of the bearings, clearance fitting is often applied because of the easiness of assembly, replacement at the time of maintenance, and the like.
However, clearance fitting causes rotational slippage between the rotation shaft and the inner rings, and shaft scraping occurs at the fitting portions of the rotation shaft and the inner rings. This causes problems of making the rotation of the rotation shaft unstable, lowering the durability, etc. These problems tend to occur when the rotation shaft is accelerated/decelerated or the rotation direction is changed while the rotation shaft is rotated by a driving unit.
FIG. 2 shows an example of a support member of a rotation shaft in a prior art. With the support member of the rotation shaft in a prior art, shown in FIG. 2, the rotation shaft 501a of a roller 501 is supported by fitting that is clearance fitting to the inner rings 601a of respective ball bearings 601 supported by panels 701. The positioning rings 603 and 503 define the positions, with respect to the axial direction, of the ball bearings 601 and the roller 501. C rings, E rings, or the like, which are generally known, can be employed as the above described positioning rings 603 and 503.
In the above described support structures in a prior art, for example, when the diameter of the rotation shaft 501a is set to φ8 and a 0-grade ball bearing in accordance with JIS B1514 standard is used for the ball bearing 601, the inner diameter of the inner ring 601a of the ball bearing 601 is φ8 [0/−0.008]. This description of [0/−0.008] represents a tolerance, wherein 0 represents the upper tolerant dimension and −0.008 represents the lower tolerant dimension. The description below is made likewise. Herein, as an example, by setting the shaft diameter of the rotation shaft 501a to φ8 [−0.01/−0.03], the gaps at the above described fitting portions become into a range from 0.01 to 0.03, which allows clearance fitting. However, as described above, acceleration/deceleration or change of rotation direction of the roller 501 causes a problem of rotation slippage between the rotation shaft 501a and the inner ring 601a due to the gap, described above, and accordingly the rotation shaft 501a and inner ring 601a are scraped. This causes problems, such as, making the rotation of the roller 510 unstable and lowering the durability.
A bearing formed in a non-circular shape is disclosed (for example, refer to Patent Document 1: Japanese Utility Model Application Publication JITSUKAI-HEI No. H02-122217), which prevents the fitting portions of an inner ring and a rotation shaft inserted into the inner ring, or the fitting portions of an outer ring and a housing into which the outer ring is inserted, from rotation slippage, as the problem described above.
Further, there are disclosed structures for attaching a bearing to which clearance fitting is applied for fitting between the inner ring thereof and a rotation shaft, as follows. A groove, which penetrates along the axial direction, is formed at, at least, one portion of either the inner ring or the rotation shaft, and a recession is provided at a part of the surface of the other one, the position of this part corresponding to the groove, so as to hold a rolling body such that the groove and the rolling body held by the recession engage with each other along the circumferential direction (for example, refer to Patent Document 2: Japanese Patent Application Publication TOKKAI No. 2002-213471).
Patent Document 1 discloses a technology which, for example, forms a protrusion from the inner ring of a bearing and a groove on the surface of a rotation shaft to be fitted to the protrusion so as to prevent rotation slippage, by the fitting between the protrusion and the groove. However, since it is necessary to machine the above-mentioned inner ring and a commercially available bearing cannot be used as it is, it increases the cost. Further, for maintenance in the field, it is necessary to use dedicated bearings, and the maintainability decreases.
Patent Document 2 discloses a technology which forms a groove on either an inner ring or a rotation shaft, the groove penetrating along the axial direction, and forms a recession at a part of the surface of the other one, the part corresponding to the groove, so as to hold a rolling body such that the groove and the rolling body held by the recession engage with each other along the circumferential direction, thereby preventing rotational slippage and smoothing the motion along the axial direction. However, the same as the technology disclosed in Patent Document 1, it is necessary to machine the inner ring, which increases the cost, and to use a dedicated bearing, which decreases the maintainability.
Taking into account a problem, as described above, an object of the present invention is to provide an image forming apparatus that allows easy assembling and maintenance and is provided with a roller having a support member that prevents rotational slippage between the inner ring of a bearing and a rotation shaft, without an increase in cost.